Using the counter of a for loop in command line parameter

Say I have (in psuedocode)
For i=1 to 10
tar cvfb /... 5*i /junk(i)
end

What I mean is that I want each successive for loop to have the block size parameter be 5 times the current counter. This isn't my actual code, just a stupid example...So the question is how do I descrive that parameter so that it uses the counter times five and have the /junk(i) be run as /junk1, /junk2, etc...?

Something like:

for i in $(seq 10)
do
  let var=${i}*5
  tar cvfb /... ${var}/junk${i}
done

> ice=1
> while [ "$ice" -le 5 ]; do mice=$((ice*2)); echo $ice $mice; ice=$((ice+1)); done

1 2
2 4
3 6
4 8
5 10

ice=1
while [ "$ice" -le 5 ]
   do 
   mice=$((ice*2))
   echo $ice $mice
   ice=$((ice+1))
done

thus, ice is the counter and mice is another variable that is a function of ice